This invention relates generally to improvements in the shaping of products from synthetic plastic resin and more particularly to enhancing the physical properties of such products.
One type of widely used synthetic resin product is extruded, thermoplastic film such as polyethylene. Attempts to improve the properties of such film are disclosed for example, in U.S. Pat. No. 3,097,915 to Doyle, wherein a conventional film extruder is utilized and the film is treated after it emerges from the slot die portion of the extruder. Other attempts to improve polyethylene film have involved chemical modification of the polyethylene resin before shaping, as disclosed for example in U.S. Pat. Nos. 4,303,571 and 4,489,034 to Jansen et al and Davison, respectively, or in the preparation of polyethylene pellets as disclosed for example in U.S. Pat. No. 4,340,550 to Ho.
Prior art methods such as those discussed above, although useful in enhancing polyethylene film for various limited purposes, involved costly chemical modification of the thermoplastic material or expensive physical treatment. It is therefore an important object of the present invention to provide a more cost effective method of improving physical properties of thermoplastic products with substantially no alteration of the product shaping process and without any supplemental treatment.